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A super fast inter-thread transfer queue.
The newest version!
/*
 * MentaQueue => http://mentaqueue.soliveirajr.com
 * Copyright (C) 2012  Sergio Oliveira Jr. ([email protected])
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.mentaqueue;

import static org.mentaqueue.util.BuilderUtils.createBuilder;

import org.mentaqueue.util.Builder;
import org.mentaqueue.util.NumberUtils;
import org.mentaqueue.util.PaddedAtomicLong;

public class AtomicQueue implements BatchingQueue {

	private final static int DEFAULT_CAPACITY = 1024 * 16;

	private final int capacity;
	private final int capacityMinusOne;
	private final E[] data;
	private long lastOfferedSeq = -1;
	private long lastPolledSeq = -1;
	private long pollCount = 0;
	private long maxSeqBeforeWrapping;
	private final PaddedAtomicLong offerSequence = new PaddedAtomicLong(-1);
	private final PaddedAtomicLong pollSequence = new PaddedAtomicLong(-1);

	@SuppressWarnings("unchecked")
	public AtomicQueue(int capacity, Builder builder) {
		NumberUtils.ensurePowerOfTwo(capacity);
		this.capacity = capacity;
		this.capacityMinusOne = capacity - 1;
		this.data = (E[]) new Object[capacity];
		for (int i = 0; i < capacity; i++) {
			this.data[i] = builder.newInstance();
		}
		this.maxSeqBeforeWrapping = calcMaxSeqBeforeWrapping();
	}

	public AtomicQueue(Builder builder) {
		this(DEFAULT_CAPACITY, builder);
	}
	
	public AtomicQueue(Class klass) {
		this(createBuilder(klass));
	}
	
	public AtomicQueue(int capacity, Class klass) {
		this(capacity, createBuilder(klass));
	}
	
	private final long calcMaxSeqBeforeWrapping() {
		return pollSequence.get() + capacity;
	}

	@Override
	public final E nextToDispatch() {
		if (++lastOfferedSeq > maxSeqBeforeWrapping) {
			// this would wrap the buffer... calculate the new one...
			this.maxSeqBeforeWrapping = calcMaxSeqBeforeWrapping();
			if (lastOfferedSeq > maxSeqBeforeWrapping) {
				lastOfferedSeq--;
				return null;				
			}
		}
		return data[(int) (lastOfferedSeq & capacityMinusOne)];
	}

	@Override
	public final void flush(boolean lazySet) {
		if (lazySet) {
			offerSequence.lazySet(lastOfferedSeq);
		} else {
			offerSequence.set(lastOfferedSeq);
		}
	}
	
	@Override
	public final void flush() {
		flush(false);
	}

	@Override
	public final long availableToPoll() {
		return offerSequence.get() - lastPolledSeq;
	}

	@Override
	public final E poll() {
		pollCount++;
		return data[(int) (++lastPolledSeq & capacityMinusOne)];
	}
	
	@Override
	public final E peek() {
		return data[(int) (lastPolledSeq & capacityMinusOne)];
	}

	@Override
	public final void donePolling(boolean lazySet) {
		if (lazySet) {
			pollSequence.lazySet(lastPolledSeq);
		} else {
			pollSequence.set(lastPolledSeq);
		}
		pollCount = 0;
	}
	
	@Override
	public final void rollback() {
		rollback(pollCount);
	}
	
	@Override
	public final void rollback(long count) {
		if (count < 0 || count > pollCount) {
			throw new RuntimeException("Invalid rollback request! polled=" + pollCount + " requested=" + count);
		}
		lastPolledSeq -= count;
		pollCount -= count;
	}
	
	@Override
	public final void donePolling() {
		donePolling(false);
	}
}